Originally in English a legal phrase (1560s) from Medieval Latin, with the sense of "to wit," introducing an explanatory or parenthetical clause, it also introduced the derogatory meaning alleged in libel cases, which led to broader meaning. As a verb, from 1706.
mid-12c., "person of ribald speech;" c. 1300, "person fond of chiding abusive language," especially a shrewish woman [Johnson defines the noun as "A clamourous, rude, mean, low, foul-mouthed woman"], from Old Norse skald "poet" (see skald).
The sense evolution might reflect the fact that Germanic poets (like their Celtic counterparts) were famously feared for their ability to lampoon and mock (as in skaldskapr "poetry," also, in Icelandic law books, "libel in verse").
The noun meaning "act of scolding" is by 1726 but seems not to have been in common use. In old law, common scold (Latin communis rixatrix) is from late 15c.
We have not sufficient adjudications to enable us to define this offence with certainty ; but probably a definition substantially correct is the following : A common scold is one, who, by the practice of frequent scolding, disturbs the repose of the neighborhood. [Joel Prentiss Bishop, "Commentaries on the Criminal Law," Boston, 1858]